Science 9

Optional Unit: Fluids and Pressure

Unit overview

What is a fluid? Why do fluids act as they do? Most people would agree that liquid water and air are fluids. Are sand and wheat fluids? What are the critical attributes or characteristic properties of fluids? Is the ability to transmit pressure equally in all directions such a property?

The sea and the air are the fluid media in which much of human activity takes place. Students have an opportunity to investigate the general properties of fluids, and how these properties influence how we conduct our lives during this unit.

Science writing and reading activities, as discussed in this Guide, should be incorporated into each lesson. When combined with the experiences students gain while working with hands-on activities in a cooperative small group setting, a variety of reading and writing activities create an environment where the opportunities for both receiving stimuli and reflecting upon those stimuli are maximized. Writing in personal reflective journals, reading from newspapers, and reporting on the activities of science class in a variety of ways are only three strategies through which students may refine their understanding of the concepts of science and develop their ability to communicate through the written word.

Science challenge, as described in this Guide, is meant to extend students' critical and creative thinking abilities in the context of the science concepts being studied. Activities involving science challenge should be incorporated into science lessons in each unit. Students should be given a chance to identify and pursue topics of their own choosing within the context of the overall theme and structure of the unit. The challenge is intended to give each student a chance to investigate an area of interest in more depth than would be possible for all students in a class to do. Science challenge is a key strategy for bringing the Adaptive Dimension to the classroom, and for encouraging independent learning.

Factors of scientific literacy that should be emphasized

Concept development

Foundational and learning objectives for Science and the Common Essential Learnings

Broaden knowledge of the characteristics of fluids.
1. Develop a model of fluids using the particle theory of matter.
2. Examine the concept of density.
3. Investigate the relationships among floating, density, displacement, volume, and buoyant force.
4. Investigate resistance to the flow of fluids and to the motion of objects in fluids.
Recognize how pressure is transmitted by fluids.
1. Understand the nature of pressure.
2. Develop ways to measure pressure.
3. Interpret transfer of pressure in fluids using the particle theory.
Strengthen understanding of physical properties of objects by applying knowledge of numbers and their interrelationships. (NUM)
1. Collect, organize, and analyze quantitative information.
2. Develop ability to read meters and scales.
3. Use benchmarks as referents for estimation.
4. Discuss with peers how estimates are made.

Suggested activities

Note: Many of the resources listed in Science: An Information Bulletin for the Middle Level - Key Resource Correlations describe activities or ideas for activities.

Wheat can be used to simulate some properties of fluids. The grains of wheat would represent the particles of matter in a liquid. When it is poured it flows. If it is confined in a box, pressure applied across the whole open surface causes the wheat to resist the pressure. Pressure applied on a point on the open surface (with a pencil for example) causes the particles to spread to allow the object exerting the pressure to enter. Ask the students to consider what happens if they do a belly flop off a diving board compared to what happens if they hit the water perpendicularly with the fingertips first.

Factors: B7, B20, C13, E13, F8, G8
Objectives: 1.1, 1.4
Assessment Techniques: written assignments, short answer test items
Instructional Methods: demonstrations, didactic questions, reflective discussion, model building
What are the forces that hold the particles of wheat together in a pile? Why won't water pile up like wheat? Will water pile up at all? Fill a small beaker or jar so that it is level full of water. Estimate how many more drops of water can be added after it is level full. Try it. What is the final shape of the surface of the water? Then carefully add paper clips to the container. How many can be added until the water overflows?

Get a small piece of aluminum foil and a small piece of waxed paper. Put a drop of water on each? Describe the shape of the drop. To 10 mL of water in a jar add five drops of dishwashing detergent. Put a drop of this water about 1 cm away from the drops already on the foil and waxed paper. Compare the shapes of the drops.

Factors: A5, B5, B10, C11, F1, G2, G6
Objectives: 1.1, 1.4
Assessment Techniques: self assessment, written assignments, oral assessment
Instructional Methods: conducting experiments, reflective discussion
Get an ice cube or block of ice (freeze water in 250 mL milk containers). Tie weights to the ends of a thin wire (about 28 gauge) so that there is enough length of wire to go across the block and down past the sides with the wire. Set the block on a stand so that the weights can hang free when the wire is placed across the block or cube of ice.

Record observations over the next few minutes. What is happening? Predict how long it will be before the effect is complete? Repeat but sprinkle salt on top of the ice along the path of the wire. Predict the effect. Repeat by changing variables such as the amount of the weight and the thickness of the wire.

Factors: A4, B7, B10, C9, F1, G8
Objectives: 1.4, 3.1
Assessment Techniques: observation checklists, presentations
Instructional Methods: demonstrations, model building, inquiry, discussion
Drill holes in the side of a large metal juice can. so that the holes are spaced at the quarter, half, and three-quarter points on the side. Make sure that all holes are the same size. Shape corks so that they fit in the holes.

Fill the can with water. Predict what will happen when the corks are removed. Remove all corks at the same time. Describe the shape of the flow from each hole. How far from the bottom of the can does each flow hit?

Predict whether the shape and distance produced by the flow from each hole will vary from the original trial if that is the only hole open. How about if one hole is plugged and two remain open?

What applications could make use of knowledge about water flow from holes in sides of containers?

Predict what would happen if this experiment were repeated with the following fluids: molasses, corn syrup, alcohol, 5-20 motor oil, transmission fluid, compressed air.
Design a device which makes use of fluid properties in its operation. Be prepared to explain how the fluid properties influence its operation.
Design a water pistol. How can the force be transmitted to the water? How can the distance the water shoots be maximized?
Get fifteen BBs and a 100 mL cylinder filled with corn syrup. Measure and record the temperature of the syrup. Measure how long it takes for a BB to fall through the syrup. Repeat the BB drop five times and calculate the average time. Measure the final temperature of the syrup and record that value.

Trade cylinders with a group that has syrup of a different temperature range. There are three sets of cylinders: cold, room temperature, and warm. Repeat the procedure in the first paragraph.

Trade cylinders once again and repeat the process.

Mark all three sets of results (average time, average temperature) on the class chart. Draw a graph of your own results. Get a copy of the class results sheet from your teacher and graph them on the same axes as your own data.

(Note to teachers: If you have 12 lab groups, prepare four cylinders at 2°C - 5°C by putting them in the fridge overnight. Prepare four cylinders with syrup at about 45° - 50°C by heating the syrup in a water bath and filling the cylinders when students are ready to begin the activity. Fill the other four cylinders with syrup at room temperature. If different size BBs or other spheres are available, the effect of size of particle on time of fall could be measured.)
With the mass of modelling clay you have been given, design and build a boat which will hold a cargo of pennies. Which designs hold the maximum loads? If you get double the mass of clay will the boat hold twice the cargo? What would happen with half the mass of clay?
What causes water pressure? Build a device to determine whether water pressure is different at various depths .
Here is a pool or lake activity. Inflate a balloon so that it is about 15 cm across. Hold the balloon under the surface of the water. Does it change shape or size? Lower the balloon in the water so that it is between 1 m and 2 m under the surface. Do you notice any change? Dive to as low as you can get with the balloon. Is there any change?
Get a set of cubes of identical size but of different materials. Measure the mass and dimensions of each cube. Calculate the volume. Arrange them in order from least massive to most massive. Place each cube in water and sketch a diagram to show how it floats with respect to the water's surface. What is the mass of the volume of water that is equal to the volume of the cubes used in this activity? Where does water fit into the range from least massive to most massive? Would water float in water?

Why does an ice cube float? What would happen if you put a bottle of full of water in a freezer overnight?

(Note to teacher: Substances appropriate for cubes are styrofoam, balsa wood, oak, cork, spruce, pine, aluminum, steel, lead, copper, modelling clay, and so on.)
Build a cube of modelling clay so that the cube will float.
Demonstrate air pressure with an aluminum pop can. Boil a small amount (10 mL) of water in the can. When the steam is coming out of the hole remove the can from the heat and stretch a piece of heavy plastic seal across the top of the can. As the can cools, the plastic wrap should seal the hole. The condensing of the steam in the can should cause the can to collapse under the pressure of the air. Rubbing the walls of the can with an ice cube can accelerate the effect.
Investigate the force of surface tension in water. How can a paper clip float on the surface of water? Why does a drop of water on a piece of waxed paper or on aluminum foil have a greater curvature than when the drop is on a piece of white note paper? How many drops of water can be placed on the surface of a penny?